Bump sinatra from 3.0.2 to 3.0.4 in /building-a-web-application

Bumps [sinatra](https://github.com/sinatra/sinatra) from 3.0.2 to 3.0.4.
- [Release notes](https://github.com/sinatra/sinatra/releases)
- [Changelog](https://github.com/sinatra/sinatra/blob/master/CHANGELOG.md)
- [Commits](sinatra/sinatra@v3.0.2...v3.0.4)

---
updated-dependencies:
- dependency-name: sinatra
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

building-a-web-application/Gemfile.lock

@@ -53,7 +53,7 @@ GEM
     postgresql_cursor (0.6.4)
       activerecord (>= 3.1.0)
     rack (2.2.8)
-    rack-protection (3.0.2)
+    rack-protection (3.0.4)
       rack
     rake (13.0.6)
     rspec (3.11.0)
@@ -70,21 +70,21 @@ GEM
       rspec-support (~> 3.11.0)
     rspec-support (3.11.1)
     ruby2_keywords (0.0.5)
-    sinatra (3.0.2)
+    sinatra (3.0.4)
       mustermann (~> 3.0)
       rack (~> 2.2, >= 2.2.4)
-      rack-protection (= 3.0.2)
+      rack-protection (= 3.0.4)
       tilt (~> 2.0)
-    sinatra-contrib (3.0.2)
+    sinatra-contrib (3.0.4)
       multi_json
       mustermann (~> 3.0)
-      rack-protection (= 3.0.2)
-      sinatra (= 3.0.2)
+      rack-protection (= 3.0.4)
+      sinatra (= 3.0.4)
       tilt (~> 2.0)
     sinatra-flash (0.3.0)
       sinatra (>= 1.0.0)
     thread_safe (0.3.6)
-    tilt (2.0.11)
+    tilt (2.2.0)
     tzinfo (2.0.5)
       concurrent-ruby (~> 1.0)
     webrick (1.7.0)